This invention relates generally to solar energy conversion devices such as flat-plate collectors, and more particularly to an improved flat-plate collector construction for retaining heat energy in such devices.
In current practice, flat-plate solar collectors used for heating air, water and various fluids are insulated beneath the collector plate and its attached fluid conduit with fiberglass or plastic foam insulation to reduce the heat loss from the back of the collector plate and its attached fluid conduit. This heat loss is a crucial factor affecting the overall efficiency of flat-plate solar collectors.
In addition to the high cost of conventional insulating materials, their limited insulating value, due to entrapped, conductive air or gas cells, places many limitations on the design and efficiency of flat-plate collectors. Until now, there has been no completely effective method for reducing the heat loss below the collector plate without incurring the weight and cost penalties of the added bulk of conventional insulating materials. Although it is evident that convective heat loss can be eliminated by the evacuation of air within the space adjacent to a heated object, this principle has not heretofore been applied to flat-plate solar collectors, primarily due to the lack of a practical means for preventing the collapse or deformation of the collector plate and fluid conduit, or the back of the collector, without the use of a massive support structure which would, in itself, introduce large conductive heat losses across the evacuated space.